Does PrEP use lead to higher STI rates among gay and bi men?

Rates of new sexually transmitted infections (STIs) are much higher among men who have sex with men (MSM) taking Truvada (tenofovir disoproxil fumarate/emtricitabine) as pre-exposure prophylaxis (PrEP) than among other MSM. More research is needed, however, to determine whether starting PrEP leads to higher STI rates among MSM.

Publishing their findings in the journal AIDS, researchers conducted a meta-analysis of 18 studies of MSM in which new STI diagnoses were reported. Five of the studies included MSM given PrEP, and 14 were conducted with MSM who were not given PrEP. (One study, the PROUD study, included both a group given PrEP immediately and a group given PrEP on a deferred basis and thus fell into both the PrEP and the non-PrEP categories of studies.)

The researchers found that the rates of new diagnoses of STIs among MSM given PrEP were 25.3 times greater for gonorrhea, 11.2 times greater for chlamydia and 44.6 times greater for syphilis, compared with the rates among MSM not given PrEP. After repeating the analysis but excluding studies conducted before 1999, the researchers found that the results were similar.

Looking to parse apart the contributing factors to the higher rate of STI diagnoses among MSM given PrEP, the meta-analysis’s authors theorized that the regular STI testing that is part of taking PrEP might have led to a higher rate of STI detection. A greater number of sex partners and a higher rate of condomless sex among those given PrEP might also have contributed to their higher STI diagnosis rate.

The study is limited by the fact that, except in the case of PROUD, the researchers compared different populations of MSM from study to study. They also compared groups that tested for STIs at different frequencies and used different variations of STI tests. Additionally, the PrEP studies specifically sought out participants engaging in high-risk sexual behaviors, while the other studies might have had different criteria with regard to sexual risk taking. However, participants in many of the non-PrEP studies were indeed recruited based on some level of reported sexual risk taking.